Photocurable liquid silicone composition and cured product thereof

ABSTRACT

A photocurable liquid silicone composition is disclosed. The photocurable liquid silicone composition comprises: (A) a straight chain organopolysiloxane having at least two alkenyl groups with 2 to 12 carbon atoms in a molecule, and not containing a mercaptoalkyl group; (B) an organopolysiloxane having at least two mercaptoalkyl groups in a molecule; (C) a branched chain organopolysiloxane, wherein alkenyl groups and mercaptoalkyl groups are not included; (D) a photo radical initiator containing a phosphorus atom; and (E) a hindered phenol compound. The photocurable liquid silicone composition is rapidly cured by irradiating with long wavelength light while providing excellent storage stability and coatability at room temperature and at low temperatures (e.g. approximately 0° C.), and provides a cured product that maintains transparency even when left under high temperature and high humidity conditions, with minimal clouding or discoloration.

TECHNICAL FIELD

The present invention relates to a photocurable liquid siliconecomposition and a cured product thereof.

BACKGROUND ART

Ultraviolet curable silicone compositions are used as adhesives andpressure sensitive adhesives for enhancing the visibility of an opticaldisplay. In recent years, thermoplastic resins such as polycarbonateshave been used for display surface covers for safety reasons, and thereis demand for a photocurable silicone composition that cures by longwavelength light (for example, visible light with a wavelength of 405nm) that is not absorbed by this type of thermoplastic resin.

For example, Patent Document 1 proposes an ultraviolet curable siliconecomposition comprising: a straight chain organopolysiloxane with alkenylgroups, an organopolysiloxane with silicon atom-bonded mercaptoalkylgroups, an acylphosphine oxide type photoreaction initiator, and anacetophenone and/or a propiophenone. However, this type of ultravioletcurable silicone composition has poor deep curing properties byirradiation of long wavelength light, along with problems withinsufficient curing, and problems in that discoloration and cloudingoccur when the cured product obtained is exposed to high temperature orhigh humidity conditions.

Furthermore, Patent Document 2 proposes an ultraviolet curable siliconepressure sensitive adhesive composition comprising: a straight chainorganopolysiloxane with alkenyl groups, an organopolysiloxane with aunique structure containing silicon atom-bonded mercaptoalkyl groups, aresin (MQ resin) that does not undergo a cross-linking reaction, and aphoto radical initiator. However, this type of ultraviolet curablesilicone composition also has poor deep curing properties by irradiationof long wavelength light, along with problems with insufficient curing,and problems in that discoloration and clouding occur when the curedproduct obtained is exposed to high temperature or high humidityconditions.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2013-253179 A

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2002-371261 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a photocurable liquidsilicone composition that is rapidly cured by irradiating with longwavelength light while providing excellent storage stability andcoatability at room temperature and at low temperatures (approximately0° C.), and to provide a cured product that maintains transparency evenwhen left under high temperature and high humidity conditions, withminimal clouding or discoloration.

Means for Solving the Problems

The photocurable liquid silicone composition of the present inventioncomprises:

(A) a straight chain organopolysiloxane with a viscosity at 23° C. of 50to 100,000 mPa·s, containing at least two alkenyl groups with 2 to 12carbon atoms in a molecule, and not containing a mercaptoalkyl group;

(B) an organopolysiloxane with a viscosity of 10 to 10,000 mPa·s at 23°C. and having at least two mercaptoalkyl groups in a molecule, in anamount such that the amount of mercaptoalkyl groups in this component is0.2 to 3 moles with regard to 1 mole of the alkenyl groups in component(A);

(C) a branched chain organopolysiloxane containing siloxane unitsrepresented by the formula: R³SiO_(3/2) (wherein R³ represents an alkylgroup with 1 to 12 carbon atoms, an aryl group with 6 to 20 carbonatoms, an aralkyl group with 7 to 20 carbon atoms, a hydroxyl group, oran alkoxy group with 1 to 6 carbon atoms) and/or siloxane unitsrepresented by the formula: SiO_(4/2), wherein the molar ratio ofsiloxane units represented by the formula: R³SiO_(3/2) and the siloxaneunits represented by the formula: SiO_(4/2) of all of the siloxane unitsin component (C) is at least 0.5, and alkenyl groups and mercaptoalkylgroups are not included;

(D) a photo radical initiator containing a phosphorus atom; and

(E) a hindered phenol compound,

wherein the amount of component (C) is 25 to 80 parts by mass, theamount of component (D) is 0.01 to 1.0 parts by mass, and the amount ofcomponent (E) is 0.001 to 1.0 parts by mass, with regard to 100 parts bymass of a total of component (A) through component (E).

The cured product of the present invention is made by irradiating andcuring the above-mentioned photocurable liquid silicone composition.

Effects of the Invention

The photocurable liquid silicone composition of the present invention israpidly cured by irradiating with long wavelength light while providingexcellent storage stability and coatability at room temperature and atlow temperatures (approximately 0° C.), and provides a cured productthat maintains transparency even when left under high temperature andhigh humidity conditions, with minimal clouding or discoloration.Furthermore, the cured product of the present invention maintainstransparency and has minimal clouding and discoloration even when leftin high temperature high humidity conditions.

MODE FOR CARRYING OUT THE INVENTION

The photocurable liquid silicone composition of the present invention isdescribed below in detail.

Component (A) is a straight chain organopolysiloxane containing at leasttwo alkenyl groups with 2 to 12 carbon atoms in a molecule, and notcontaining a mercaptoalkyl group. Preferable examples of the alkenylgroup in component (A) include vinyl groups, allyl groups, butenylgroups, pentenyl groups, hexenyl groups, heptenyl groups, octenylgroups, nonenyl groups, decenyl groups, undecenyl groups, and dodecenylgroups, but from the perspective of economics and reactivity, vinylgroups, allyl groups, hexenyl groups, and octenyl groups are preferable.Furthermore, examples of silicon atom-bonded groups other than alkenylgroups in component (A) include: alkyl groups with 1 to 12 carbon atomssuch as methyl groups, ethyl groups, propyl groups, butyl groups, pentylgroups, hexyl groups, heptyl groups, octyl groups, nonyl groups, decylgroups, undecyl groups, dodecyl groups, and the like; aryl groups with 6to 12 carbon atoms such as phenyl groups, tolyl groups, xylyl groups,and the like; aralkyl groups with 7 to 12 carbon atoms such as benzylgroups, phenethyl groups, and the like; halogen substituted alkyl groupswith 1 to 12 carbon atoms such as 3-chloropropyl groups,3,3,3-trifluoropropyl groups, and the like; but from the perspective ofeconomics and heat resistance, methyl groups are preferable.Furthermore, the silicon atom in component (A) may be bonded to a smallamount of hydroxyl groups or alkoxy groups such as methoxy groups,ethoxy groups, n-propoxy groups, i-propoxy groups, n-butoxy groups,sec-butoxy groups, tert-butoxy groups and the like.

The viscosity of component (A) at 23° C. is within a range of 50 to100,000 mPa·s, preferably within a range of 100 to 100,000 mPa·s,alternatively within a range of 100 to 50,000 mPa·s, and alternativelywithin a range of 100 to 10,000 mPa·s. This is because if the viscosityof component (A) is not less than the lower limit of the aforementionedrange, the mechanical properties of the cured product obtained will beenhanced; however, on the other hand, if the viscosity is not more thanthe upper limit of the aforementioned range, the coatability of thecomposition obtained will be enhanced.

Component (A) can be represented, for example, by the general formula:

R¹ ₃SiO(R¹ ₂SiO)_(m)SiR¹ ₃.

In the formula, R¹ is the same or different monovalent hydrocarbon grouphaving 1 to 12 carbon atoms, and examples include alkyl groups having 1to 12 carbon atoms such as methyl groups, ethyl groups, propyl groups,butyl groups, pentyl groups, hexyl groups, heptyl groups, octyl groups,nonyl groups, decyl groups, undecyl groups, and dodecyl group, and thelike; alkenyl groups having 2 to 12 carbon atoms such as vinyl groups,allyl groups, butenyl groups, pentenyl groups, hexenyl groups, heptenylgroups, octenyl groups, nonenyl groups, decenyl groups, undecenylgroups, dodecenyl groups, and the like; aryl groups having 6 to 12carbon atoms such as phenyl groups, tolyl groups, and xylyl groups, andthe like; aralkyl groups having 7 to 12 carbon atoms such as benzylgroups, phenethyl groups, and the like; halogen-substituted alkyl groupshaving 1 to 12 carbon atoms, such as a 3-chloropropyl groups,3,3,3-trifluoropropyl groups, and the like; however, at least two R¹ ina molecule are alkenyl groups described above. Furthermore, m in theformula is an integer of 1 or higher, wherein the viscosity of component(A) at 23° C. is within a range of 50 to 100,000 mPa·s.

This type of component (A) can be a mixture of two or more types oforganopolysiloxanes represented by the following general formulas. Notethat in the formulas, Me, Vi, and Ph represent methyl groups, vinylgroups, and phenyl groups, respectively; wherein, m′ and m″ representintegers that are 1 or higher such that the viscosity at 23° C. iswithin a range of 50 to 100,000 mPa·s, and m′″ is an integer of 2 orhigher such that the viscosity at 23° C. is within a range of 50 to100,000 mPa·s.

Me₂ViSiO(Me₂SiO)_(m′)SiMe₂Vi

Me₂ViSiO(Me₂SiO)_(m′)(MePhSiO)_(m″)SiMe₂Vi

Me₂ViSiO(Me₂SiO)_(m′)(Ph₂SiO)_(m″)SiMe₂Vi

Me₂ViSiO(Me₂SiO)_(m′)(MeViSiO)_(m″)SiMe₂Vi

Me₃SiO(Me₂SiO)_(m′)(MeViSiO)_(m′″)SiMe₃

Me₃SiO(MeViSiO)_(m′″)SiMe₃

Component (B) is an organopolysiloxane with at least two mercaptoalkylgroups in a molecule, and is a component for curing this composition byreacting with the alkenyl groups in component (A) under irradiation.Examples of the mercaptoalkyl group in component (B) include3-mercaptopropyl groups, 4-mercaptobutyl groups, and 6-mercaptohexylgroups. Furthermore, examples of silicon atom-bonded groups other thanmercaptoalkyl groups in component (B) include: alkyl groups with 1 to 12carbon atoms such as methyl groups, ethyl groups, propyl groups, butylgroups, pentyl groups, hexyl groups, heptyl groups, octyl groups, nonylgroups, decyl groups, undecyl groups, dodecyl groups, and the like; arylgroups with 6 to 12 carbon atoms such as phenyl groups, tolyl groups,xylyl groups, and the like; aralkyl groups with 7 to 12 carbon atomssuch as benzyl groups, phenethyl groups, and the like; halogensubstituted alkyl groups with 1 to 12 carbon atoms such as3-chloropropyl groups, 3,3,3-trifluoropropyl groups, and the like; butfrom the perspective of economics and heat resistance, methyl groups arepreferable. Furthermore, the silicon atom in component (B) may be bondedto a small amount of hydroxyl groups or alkoxy groups such as methoxygroups, ethoxy groups, n-propoxy groups, i-propoxy groups, n-butoxygroups, sec-butoxy groups, tert-butoxy groups and the like.

The viscosity of component (B) at 23° C. is within a range of 10 to10,000 mPa·s, preferably within a range of 10 to 1,000 mPa·s, andalternatively within a range of 10 to 500 mPa·s. This is because, if theviscosity of component (B) is not less than the lower limit of theaforementioned range, the mechanical properties of the cured productobtained will be enhanced; however, if, on the other hand, the viscosityis not more than the upper limit of the aforementioned range, thetransparency and coatability of the composition obtained will beenhanced.

Examples of this type of component (B) can include, for example, (B1)straight chain organopolysiloxanes represented by the general formula:

R² ₃SiO(R² ₂SiO)_(n)SiR² ₃

and/or (B2) branched chain organopolysiloxanes represented by theaverage unit formula:

(R² ₃SiO_(1/2))_(a)(R² ₂SiO_(2/2))_(b)(R²SiO_(3/2))_(c)(SiO_(4/2))_(d)·

In the formula, R² is the same or different monovalent hydrocarbon groupwith 1 to 12 carbon atoms that does not have a mercaptoalkyl group or analiphatic unsaturated bond. Examples of the mercaptoalkyl groups are thesame groups as described above. Furthermore, the monovalent hydrocarbongroups that do not have an aliphatic unsaturated bond are the same asdescribed above, with examples including alkyl groups with 1 to 12carbon atoms, aryl groups with 6 to 12 carbon atoms, aralkyl groups with7 to 12 carbon atoms, and halogen substituted alkyl groups with 1 to 12carbon atoms However, at least two of all R² groups are mercaptoalkylgroups described above.

Furthermore, n in the formula is an integer of 1 or higher, wherein theviscosity of component (B1) at 23° C. is 10 to 10,000 mPa·s.

Furthermore, in the formula, a, b, c, and d are numbers from 0 to 1, andthe total of a, b, c, and d are 1 in a molecule. However, c or d is anumber that exceeds 0.

Component (B1) can be a mixture of two or more types oforganopolysiloxanes represented by the following general formulas. Notethat in the formulas, Me, Ph, and Thi represent methyl groups, phenylgroups, and 3-mercaptopropyl groups, respectively; n′ and n″ representintegers that are 1 or higher, respectively such that the viscosity at23° C. is within a range of 10 to 10,000 mPa·s, and n′″ is an integer of2 or higher such that the viscosity at 23° C. is within a range of 10 to10,000 mPa·s.

Me₃SiO(Me₂SiO)_(n′)(MeThiSiO)_(n′″)SiMe₃

Me₃SiO(MePhSiO)_(n′)(MeThiSiO)_(n′″)SiMe₃

Me₃SiO(Me₂SiO)_(n′)(Ph₂SiO)_(n″)(MeThiSiO)_(n′″)SiMe₃

Component (B2) can be one type or a mixture of two or more types oforganopolysiloxanes represented by the following average unit formulas.Note that in the formula, Me, Ph, and Thi represent methyl groups,phenyl groups, and 3-mercaptopropyl groups, respectively; wherein, a′,b′, b″, c′, and d′ represent numbers from 0 to 1, respectively (however,0 is not included), and the total of a′, b′, b″, c′, and d′ is 1 in amolecule.

(Me₃SiO_(1/2))_(a′)(Me₂SiO_(2/2))_(b′)(MeThiSiO_(2/2))_(b″)(MeSiO_(3/2))_(c′)

(Me₃SiO_(1/2))_(a′)(MeThiSiO_(2/2))_(b′)(MeSiO_(3/2))_(c′)

(Me₃SiO_(1/2))_(a′)(MeThiSiO_(2/2))_(b′)(ThiSiO_(3/2))_(c′)

(Me₃SiO_(1/2))_(a′)(Me₂SiO_(2/2))_(b′)(ThiSiO_(3/2))_(c′)

(Me₃SiO_(1/2))_(a′)(Me₂SiO_(2/2))_(b′)(Ph₂SiO_(2/2))_(b″)(ThiSiO_(3/2))_(c′)

(Me₃SiO_(1/2))_(a′)(MeThiSiO_(2/2))_(b′)(PhSiO_(3/2))_(c′)

(Me₃SiO_(1/2))_(a′)(ThiSiO_(3/2))_(c′)

(Me₂SiO_(2/2))_(b′)(MeThiSiO_(2/2))_(b″)(MeSiO_(3/2))_(c′)

(MeThiSiO_(2/2))_(b′)(MeSiO_(3/2))_(c′)

(Me₂SiO_(2/2))_(b′)(ThiSiO_(3/2))_(c′)

(Me₂SiO_(2/2))_(b′)(MeThiSiO_(2/2))_(b″)(ThiSiO_(3/2))_(c′)

(Me₃SiO_(1/2))_(a′)(MeThiSiO_(2/2))_(b′)(SiO_(4/2))_(d′)

The amount of component (B) is such that the amount of mercaptoalkylgroups in this component is within a range of 0.2 to 3 moles, preferablywithin a range of 0.5 to 2 moles, and alternatively within a range of0.5 to 1.5 moles, with regard to 1 mole of the alkenyl groups incomponent (A). This is because if the amount of component (B) is notless than the lower limit of the aforementioned range, the compositionobtained will sufficiently cure; however, if, on the other hand, theamount is not more than the upper limit of the aforementioned range, themechanical properties of the cured product obtained will be enhanced.

Component (C) is a branched chain organopolysiloxane containing siloxaneunits represented by the formula: R³SiO_(3/2) and/or siloxane unitsrepresented by the formula: SiO_(4/2), and not having alkenyl groups andmercaptoalkyl groups. In the formula, R³ is alkyl groups with 1 to 12carbon atoms, aryl groups with 6 to 20 carbon atoms, aralkyl groups with7 to 20 carbon atoms, hydroxyl groups, or alkoxy groups with 1 to 6carbon atoms, and specific examples include alkyl groups such as methylgroups, ethyl groups, propyl groups, butyl groups, pentyl groups, hexylgroups, heptyl groups, octyl groups, nonyl groups, decyl groups, undecylgroups, dodecyl groups, and the like; aryl groups such as phenyl groups,tolyl groups, xylyl groups, and the like; aralkyl groups such as benzylgroups, phenethyl groups, and the like; hydroxyl groups; and alkoxygroups such as methoxy groups, ethoxy groups, propoxy groups, and thelike.

Component (C) contains siloxane units represented by the formula:R₃SiO_(3/2) and/or siloxane units represented by the formula: SiO_(4/2,)but other siloxane units that may be included are siloxane unitsrepresented by the formula: R³ ₂SiO_(2/2) and siloxane units representedby the formula: R³ ₃SiO_(1/2.) Note that in the formula, R³ are the samegroups as described above. However, the molar ratio of siloxane unitsrepresented by the formula: R³SiO_(3/2) and siloxane units representedby the formula: SiO_(4/2) with regard to all of the siloxane units incomponent (C) is at least 0.5. This is because if the value is not lessthan the aforementioned lower limit, the pressure sensitive adhesion ofthe cured product obtained will be higher. Incidentally, the upper limitof this value is not restricted, but is preferably 0.65 or lower, due togood solubility with other organopolysiloxanes.

Furthermore, while the molecular weight of component (C) is not limited,the weight average molecular weight as measured by the gel permeationchromatography method is preferably within a range of 2,000 to 50,000.This is because if the weight average molecular weight of component (C)is not less than the lower limit of the aforementioned range, thepressure sensitive adhesion properties of the cured product obtainedwill be enhanced, but on the other hand, if the weight average molecularweight is not more than the upper limit of the aforementioned range, themoldability of the composition obtained will be enhanced.

Component (C) can be one type or a mixture of two or more types oforganopolysiloxanes represented by the following average unit formulas.Note that in the formula, Me and Ph represent methyl groups and phenylgroups, respectively; wherein, e, f, g, g′, and h each represent numbersfrom 0 to 1 that express the ratio of the constitutional units (however,0 is not included), and the total of e, f, g, g′, and h is 1 in amolecule.

(Me₃SiO_(1/2))_(c)(Me₂SiO_(2/2))_(f)(MeSiO_(3/2))_(g)

(Me₃SiO_(1/2))_(e)(Me₂SiO_(2/2))_(f)(SiO_(4/2))_(h)

(Me₃SiO_(1/2))_(e)(MeSiO_(3/2))_(g)

(Me₃SiO_(1/2))_(e)(SiO_(4/2))_(h)

(Me₃SiO_(1/2))_(e)(Me₂SiO_(2/2))_(f)(MeSiO_(3/2))_(g)(SiO_(4/2))_(h)

(Me₃SiO_(1/2))_(e)(MeSiO_(3/2))_(g)(SiO_(4/2))_(h)

(Me₃SiO_(1/2))_(e)(PhSiO_(3/2))_(g)(SiO_(4/2))_(h)

(Me₃SiO_(1/2))_(e)(MeSiO_(3/2))_(g)(PhSiO_(3/2))_(g′)

(Me₃SiO_(1/2))_(e)(Ph₂SiO_(2/2))_(f)(SiO_(4/2))_(h)

The amount of component (C) is within a range of 25 to 80 parts by mass,preferably within a range of 40 to 80 parts by mass, or alternativelywithin range of 40 to 65 parts by mass, with regard to 100 parts by massof a total of component (A) through component (E). This is because ifthe amount of component (C) is not less than the lower limit of theaforementioned range, the curing properties of the composition obtainedwill be favorable and the transparency of the cured product obtainedwill be favorable; however, if, on the other hand, the amount is notmore than the upper limit of the aforementioned range, the pressuresensitive adhesive properties of the cured product obtained will befavorable.

Component (D) is a photo radical initiator containing a phosphorus atomthat promotes curing of this composition. As the component (D), forexample, a photo radical initiator having a P═O bond in the molecule canbe mentioned, and specific examples includediphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (trade name Darocur TPO,manufactured by BASF Corporation),ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (trade name IrgacureTPO-L, manufactured by BASF Corporation), a 50/50 (parts by mass)mixture of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and2-hydroxy-2-methyl-1-phenylpropanone (trade name Darocur 4265,manufactured by BASF Corporation), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (trade name Irgacure 819,manufactured by BASF Corporation), and a mixture ofethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide andphenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (trade name Irgacure2100, manufactured by BASF Corporation). Furthermore, the photo radicalinitiator having a P=0 bond can be formulated as a mixture that isdissolved in a liquid photo radical initiator not having a P═O bond,such as 2-hydroxy-2-methyl-1-phenyl-propan-1-one at an arbitrary ratio.

The amount of component (D) is within a range of 0.01 to 1.0 parts bymass, preferably within a range of 0.05 to 0.5 parts by mass, oralternatively within a range of 0.05 to 0.2 parts by mass, with regardto 100 parts by mass of a total of component (A) through component (E).This is because if the amount of component (D) is not less than thelower limit of the aforementioned range, the curing properties of thecomposition obtained will the favorable; however, if, on the other hand,the amount is not more than the upper limit of the aforementioned range,the heat resistance and light resistance of the cured product obtainedwill be favorable.

Component (E) is a hindered phenol compound for maintaining favorablestorage stability of the composition, and to provide heat resistance tothe cured product. Examples of component (E) include2,6-bis(hydroxymethyl)-p-cresol, 2,6-di-tert-butyl-4-methylphenol,2,6-di-tert-butyl-4-hydroxymethylphenol, pentaerythritoltetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,2,4-dimethyl-6-(1-methylpentadecyl)phenol,diethyl[{3,5-bis(1,1-di-tert-butyl-4-hydroxyphenyl)methyl}phosphonate,3,3′,3″,5,5′,5″-hexane-tert-butyl-4-a,a′,a″-(mesitylene-2,4,6-tolyl)tri-p-cresol, 4,6-bis(octylthiomethyl)-o-cresol, ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate],hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

The amount of component (E) is within a range of 0.001 to 1 parts bymass, preferably within a range of 0.01 to 1 parts by mass, oralternatively within range of 0.01 to 0.5 parts by mass, with regard to100 parts by mass of a total of component (A) through component (E).This is because if the amount of component (E) is not less than thelower limit of the aforementioned range, the storage stability of thecomposition obtained will the favorable; however, if, on the other hand,the amount is not more than the upper limit of the aforementioned range,the heat resistance and light resistance of the cured product obtainedwill be favorable.

In order to enhance the transparency of the cured product obtained underhigh temperature and high humidity conditions, the composition cancontain (F) an organopolysiloxane having an organic group with an etherbond and an alkenyl group with 2 to 12 carbon atoms in a molecule, butnot having a mercaptoalkyl group. The organic group having an ether bondcan be an alkyl group containing polyethylene oxide, or an alkyl groupcontaining polyethylene oxide and polypropylene oxide, and for example,can be represented by the general formula:

—(CH₂CHR⁴CH₂)−(OC₂H₄)_(p)(OC₃H₆)_(q)OR⁵.

In the formula, R⁴ represents a hydrogen atom or a methyl group.Furthermore, in the formula, R⁵ represents a hydrogen atom or an alkylgroup with 1 to 3 carbon atoms, such as a methyl group, ethyl group, orpropyl group. Furthermore, in the formula, p is an integer from 1 to100, inclusive, and q is an integer from 0 to 50, inclusive.

Furthermore, examples of the alkenyl group in component (F) includevinyl groups, allyl groups, butenyl groups, pentenyl groups, hexenylgroups, heptenyl groups, octenyl groups, nonenyl groups, decenyl groups,undecenyl groups, and dodecenyl groups, but vinyl groups are preferable.

Furthermore, examples of silicon atom-bonded groups other than organicgroups with an ether bond and alkenyl groups with 2 to 12 carbon atomsin component (F) include: alkyl groups with 1 to 12 carbon atoms such asmethyl groups, ethyl groups, propyl groups, butyl groups, pentyl groups,hexyl groups, heptyl groups, octyl groups, nonyl groups, decyl groups,undecyl groups, dodecyl groups, and the like; aryl groups with 6 to 12carbon atoms such as phenyl groups, tolyl groups, xylyl groups, and thelike; aralkyl groups with 7 to 12 carbon atoms such as benzyl groups,phenethyl groups, and the like; halogen substituted alkyl groups with 1to 12 carbon atoms such as 3-chloropropyl groups, 3,3,3-trifluoropropylgroups, and the like; but from the perspective of economics and heatresistance, methyl groups are preferable.

While the viscosity of component (F) at 23° C. is not limited, it ispreferably within a range of 10 to 10,000 mPa·s.

The organopolysiloxane of component (F) can be represented, for example,by the general formula:

R⁶ ₃SiO(R⁶ ₂SiO)_(x)SiR⁶ ₃

In the formula, R⁶ represents the same or different monovalenthydrocarbon group with 1 to 12 carbon atoms or an organic group havingan ether bond. Examples of the organic group having an ether bond arethe same groups as described above. Furthermore, the monovalenthydrocarbon groups with 1 to 12 carbon atoms are the same as describedabove, such as alkyl groups with 1 to 12 carbon atoms, alkenyl groupswith 2 to 12 carbon atoms, aryl groups with 6 to 12 carbon atoms,aralkyl groups with 7 to 12 carbon atoms, and halogen substituted alkylgroups with 1 to 12 carbon atoms. However, at least one R⁶ in a moleculeis the organic group having an ether bond described above, and at leastone R⁶ is the alkenyl group described above. Furthermore, x is aninteger that is 1 or higher, and preferably is a value such that theviscosity at 23° C. is within a range of 10 to 10,000 mPa·s.

This type of component (F) can be one type or a mixture of two or moretypes of organopolysiloxanes expressed by the following generalformulas. Note that, in the formulas, Me, Vi, Hex, EO, and PO representa methyl group, vinyl group, hexenyl group, oxyethylene group, oroxypropylene group, respectively; wherein, x′, x″, and x′″ are allintegers 1 or higher, p is an integer from 1 to 100, inclusive, and q′is an integer from 1 to 50, inclusive.

Me(EO)_(p)OC₃H₆Me₂SiO(Me₂SiO)_(x′)(MeViSiO)_(x″)SiMe₂C₃H₆(EO)_(p)OMe

Me(EO)_(p)OCH₂CH(Me)CH₂Me₂SiO(Me₂SiO)_(x′)(MeViSiO)_(x″)SiMe₂CH₂CH(Me)CH₂(EO)_(p)OMe

H(EO)_(p)OC₃H₆Me₂SiO(Me₂SiO)_(x′)(MeViSiO)_(x″)SiMe₂C₃H₆(EO)_(p)OH

H(EO)_(p)OCH₂CH(Me)CH₂Me₂SiO(Me₂SiO)_(x′)(MeViSiO)_(x″)SiMe₂CH₂CH(Me)CH₂(EO)_(p)OH

Me(PO)_(q)(EO)_(p)OC₃H₆Me₂SiO(Me₂SiO)_(x′)(MeViSiO)_(x″)SiMe₂C₃H₆(EO)_(p)(PO)_(q)OMe

Me(PO)_(q)(EO)_(p)OCH₂CH(Me)CH₂Me₂SiO(Me₂SiO)_(x′)(MeViSiO)_(x)^(″)SiMe₂CH₂CH(Me) CH₂(EO)_(p)(PO)_(q)OMe

H(PO)_(q)(EO)_(p)OC₃H₆Me₂SiO(Me₂SiO)_(x′)(MeViSiO)_(x″)SiMe₂C₃H₆(EO)_(p)(PO)_(q)OH

H(PO)_(q)(EO)_(p)OCH₂CH(Me)CH₂Me₂SiO(Me₂SiO)_(x′)(MeViSiO)_(x″)SiMe₂CH₂CH(Me)CH₂(EO)_(p)(PO)_(q)OH

Me₃SiO(Me₂SiO)_(x′)(MeViSiO)_(x″)[Me(Me(EO)_(p)OC₃H₆)SiO]_(x′″)SiMe₃

Me₃SiO(Me₂SiO)_(x′)(MeViSiO)_(x″)[Me(H(EO)_(p)OC₃H₆)SiO]_(x′″)SiMe₃

Me₃SiO(Me₂SiO)_(x′)(MeHexSiO)_(x″)[Me(Me(EO)_(p)OC₃H₆)SiO]_(x′″)SiMe₃

Me₃SiO(Me₂SiO)_(x′)(MeHexSiO)_(x″)[Me(H(EO)_(p)OC₃H₆)SiO]_(x′″)SiMe₃

Me₃SiO(Me₂SiO)_(x′)(MeViSiO)_(x″)[Me(Me(EO)_(p)OC₃H₆)SiO]_(x′″)SiMe₂Vi

Me₃SiO(Me₂SiO)_(x′)(MeViSiO)_(x″)[Me(H(EO)_(p)OC₃H₆)SiO]_(x′″)SiMe₂Vi

Me₂ViSiO(Me₂SiO)_(x′)[Me(Me(EO)_(p)OC₃H₆)SiO]_(x″)SiMe₂Vi

Me₂ViSiO(Me₂SiO)_(x′)[Me(H(EO)_(p)OC₃H₆)SiO]_(x″)SiMe₂Vi

The method for producing component (F) is not limited, and can include,for example: a method of causing a hydrosilylation reaction between anorganopolysiloxane containing a silicon atom-bonded hydrogen atom and anether compound having an aliphatic unsaturated group to produce anorganopolysiloxane having an ether group, then causing an equilibriumreaction between this organopolysiloxane and organopolysiloxane havingan alkenyl group, in the presence of a base; and a method of causing ahydrosilylation reaction between an organopolysiloxane containing asilicon atom-bonded hydrogen atom and an ether compound having analiphatic unsaturated group to produce an organopolysiloxane having anether group, then causing a hydrosilylation reaction between the excessof silicon atom-bonded hydrogen atoms and an organic compound having twoaliphatic unsaturated groups.

The amount of component (F) is not restricted, but the amount ispreferably within a range of 1 to 50 parts by mass, alternatively withina range of 1 to 30 parts by mass, and alternatively within a range of 1to 15 parts by mass, with regard to 100 parts by mass of a total ofcomponent (A) through component (E), because the curing properties andthe storage stability of the composition will be favorable, and thetransparency of the cured product at high temperature and high humiditycan be enhanced.

In order to reduce the cross-linking density of the cured productobtained, thereby enhancing the mechanical properties and the pressuresensitive adhesion, the present composition may contain (G) an organiccompound having one aliphatic unsaturated bond and not having a siloxanebond, in a molecule. Component (G) is preferably an organic compounddemonstrating favorable solubility with component (A) through component(E), along with favorable storage stability and therefore a boilingpoint of 200° C. or higher at 1 atm., for example. Examples of component(G) include straight chain aliphatic olefins such as dodecene,tetradecene, hexadecene, octadecene, and the like; cyclic aliphaticolefins such as 4-phenyl-1-cyclohexene, and the like; and unsaturatedalcohol such as 9-decen-1-ol, oleyl alcohol, terpen-4-ol, and the like.

The amount of component (G) is not restricted, but the amount ispreferably within a range of 0.1 to 10 parts by mass, and alternativelywithin a range of 0.1 to 5 parts by mass, with regard to 100 parts bymass of a total of component (A) through component (E), because thecuring properties of the composition will be favorable, and themechanical properties of the cured product obtained will be favorable.

Within an extent that the object of the present invention is nothindered, the present composition may contain (H) a branchedorganopolysiloxane containing siloxane units represented by the formula:R⁷SiO_(3/2) and/or siloxane units represented by the formula: SiO₂,having an alkenyl group, but not having a mercaptoalkyl group. In theformula, R⁷ represents an alkyl group with 1 to 12 carbon atoms, analkenyl group with 2 to 12 carbon atoms, a hydroxyl group, or an alkoxygroup with 1 to 6 carbon atoms. Examples of the alkyl group includemethyl groups, ethyl groups, propyl groups, butyl groups, pentyl groups,hexyl groups, heptyl groups, octyl groups, nonyl groups, decyl groups,undecyl groups, and dodecyl groups. Furthermore, examples of the alkenylgroup include vinyl groups, allyl groups, butenyl groups, pentenylgroups, hexenyl groups, heptenyl groups, octenyl groups, nonenyl groups,decenyl groups, undecenyl groups, and dodecenyl groups. Furthermore,examples of the alkoxy group include methoxy groups, ethoxy groups,propoxy groups, and butoxy groups. Note that if the siloxane unitsrepresented by the formula: R⁷SiO_(3/2) does not have an alkenyl group,the other siloxane units must be siloxane units represented by theformula: R⁸ ₃SiO_(1/2) and/or siloxane units represented by the formula:R⁸ ₂SiO_(2/2.) Note that in the formula, R⁸ represents an alkyl groupwith 1 to 12 carbon atoms, an alkenyl group with 2 to 12 carbon atoms, ahydroxyl group, or an alkoxy group with 1 to 6 carbon atoms, andexamples are the same as described above. Note that at least one R⁸ in amolecule is an alkenyl group.

Component (H) can be one type or a mixture of two or more types oforganopolysiloxanes represented by the following average unit formulas.Note that in the formulas, Me and Vi represent methyl groups and vinylgroups, respectively; wherein, i, i′, j, j′, k, and l each representnumbers from 0 to 1 that express the ratio of the constitutional units(however, 0 is not included), but the total of i, i′, j, j′, k, and 1 is1 in a molecule.

(Me₃SiO_(1/2))_(i)(Me₂ViSiO_(1/2))_(i′)(MeSiO_(3/2))_(k)

(Me₂ViSiO_(1/2))_(i)(Me₂SiO_(2/2))_(j)(MeSiO_(3/2))_(k)

(Me₃SiO_(1/2))_(i)(Me₂ViSiO_(1/2))_(i′)(Me₂SiO_(2/2))_(j)(MeSiO_(3/2))_(k)

(Me₃SiO_(1/2))_(i)(Me₂ViSiO_(1/2))_(i′)(MeViSiO_(2/2))_(j)(MeSiO_(3/2))_(k)

(Me₃SiO_(1/2))_(i)(Me₂SiO_(2/2))_(j)(MeViSiO_(2/2))_(j′)(MeSiO_(3/2))_(k)

(Me₃SiO_(1/2))_(i)(Me₂ViSiO_(1/2))_(i′)(SiO_(4/2))_(l)

(Me₂ViSiO_(1/2))_(i)(SiO_(4/2))_(l)

(Me₃SiO_(1/2))_(i)(MeViSiO_(2/2))_(j)(SiO_(4/2))_(l)

(Me₂ViSiO_(1/2))_(i)(Me₂SiO_(2/2))_(j)(SiO_(4/2))_(l)

(Me₃SiO_(1/2))_(i)(Me₂ViSiO_(1/2))_(i′)(Me₂SiO_(2/2))_(j)(SiO_(4/2))_(l)

(Me₂ViSiO_(1/2))_(i)(Me₂SiO_(2/2))_(j)(MeViSiO_(2/2))_(j′)(SiO_(4/2))_(l)

(Me₂ViSiO_(1/2))_(i)(Me₂SiO_(2/2))_(j)(MeSiO_(3/2))_(k)(SiO_(4/2))₁

While the amount of component (H) is not limited, the ratio of alkenylgroups in component (H) with regard to the total of alkenyl groups incomponent (A) and the alkenyl groups in component (H) is preferably lessthan 50%, alternatively less than 20%, and alternatively less than 10%.This is because if the amount of component (H) is not less than theupper limit of the aforementioned range, there will be a significantreduction in the mechanical properties of the cured product obtained,particularly the tensile elongation at break.

Furthermore, so long as the object of the present invention is nothindered, the composition can contain conventionally known additives asnecessary, in addition to the aforementioned components, with examplesincluding: metal oxide fine powders such as fumed silica, wet silica,and the like; adhesion promoters such as vinyl triethoxysilane, allyltrimethoxysilane, allyl triethoxysilane, 3-glycidoxypropyltrimethoxysilane, and the like; low molecular weight siloxane containingan alkenyl group as a reactive diluent, such as1,1,3,3-tetramethyl-1,3-divinyldisiloxane,1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, and the like;and heat resistance enhancing agents such asN-nitrosophenylhydroxylamine aluminum salt, and the like.

While the viscosity of the present composition at 23° C. is not limited,it is preferably 100,000 mPa·s or less, alternatively within a range of100 to 100,000 mPa·s, and alternatively within a range of 500 to 10,000mPa·s. This is because if the viscosity of the composition is not lessthan the lower limit of the aforementioned range, the mechanicalproperties of the cured product obtained will be favorable; however, if,on the other hand, the viscosity is not more than the upper limit of theaforementioned range, the coatability of the composition obtained willbe enhanced and the formation of voids in the cured product can beavoided.

The present composition can be produced by blending to uniformitycomponent (A) through component (E), and if necessary, other arbitrarycomponents. When preparing this composition, mixing can be performed atroom temperature using various types of mixers or kneaders, and ifnecessary, mixing can be performed while heating. Furthermore, the orderof combining the various components is not restricted, and mixing can beperformed in any order. On the other hand, in order to avoid the effectof curing during preparation of the composition, it is recommended thatpreparation be performed in a location without mixing of light with awavelength of 450 nm or less, or in an area where mixing of theaforementioned light is restricted as far as possible.

The present composition can be cured by light irradiation. While thelight used for curing the composition can be ultraviolet light orvisible light, for example, the wavelength of the light is preferablywithin a range of 250 to 500 nm, with the composition thereof havingpreferable curing properties by visible light with a wavelength of 400nm or longer (for example, an LED light source with a wavelength of 405nm).

The present composition is useful as various types of potting agents,sealing agents, and adhesives, and the cured product thereof has minimaldiscoloration and does not readily cloud under high temperature or hightemperature and high humidity conditions, and therefore is suitably usedas a material for forming intermediate layers between the image displaypart and the protective part of an image display device.

The present composition cures at room temperature, and therefore can besuitably used for coating substrates with poor heat resistance. The typeof substrate is generally a transparent substrate such as glass, andsynthetic resin films, sheets, and coatings, and the like. Furthermore,the application method of the composition can be, for example, gravurecoating, microgravure coating, slit coating, slot die coating, screenprinting, or comma coating.

Next, the cured product of the present invention will be described indetail.

The cured product of the present invention is made by irradiating lightand curing the photocurable liquid silicone composition. While the shapeof the cured product is not particularly limited, examples includesheets, films, tapes, and lumps. Furthermore, integrating with varioustypes of substrates is also possible.

The forming method of the cured product can be a method of applying thecomposition to a film shaped substrate, tape shaped substrate, or sheetshaped substrate, then curing by irradiating light forming a cured filmmade of the cured product on the surface of the substrate. The filmthickness of the cured film is not restricted, but is preferably 1 to3000 μm, or 40 to 3000 μm.

EXAMPLES

The photocurable liquid silicone composition and cured product thereofis described below in further detail using examples. Note that in theformulas, Me, Vi, Ph, Thi, and EO indicate methyl groups, vinyl groups,phenyl groups, 3-thiolpropyl groups, and oxyethylene groups,respectively. Furthermore, in the examples, measurements and evaluationswere performed as described below.

<Viscosity of Photocurable Liquid Silicone Composition and VariousComponents>

Each viscosity (mPa·s) at 23° C. of the photocurable liquid siliconecomposition and various components was measured using an E typeviscometer VISCONIC EMD manufactured by TOKIMEC CORPORATION.

<Weight Average Molecular Weight of Organopolysiloxane>

The weight average molecular weight of the organopolysiloxane calculatedas standard polystyrene was determined by gel permeation chromatographyusing a light scattering detector.

<Chemical Structure of Organopolysiloxane>

The chemical structure of the organopolysiloxane was identified usingnuclear magnetic resonance spectral analysis.

<Appearance of Photocurable Liquid Silicone Composition>

The appearance of the photocurable liquid silicone composition wasvisually observed and evaluated as described below.

A: Transparent

B: Slightly cloudy

<Curing Properties of Photocurable Liquid Silicone Composition>

The photocurable liquid silicone composition is filled between twopolycarbonate sheets with a thickness of 2 mm such that the thicknessafter curing is approximately 200 μm (fill area: 20×20 mm²), and thenLED light with a wavelength of 405 nm was irradiated at an intensity of50 mW/cm² for 40 seconds. The two polycarbonate sheets were peeled off,the composition was observed to determine if fluidity was lost and thecomposition was cured, and then evaluation was performed as describedbelow.

A: Cured

B: Not cured

<Transparency of Cured Product>

The photocurable liquid silicone composition is filled in a die withregular shaped depressions such that the thickness after curing isapproximately 500 μm (fill area: 40×40 mm²), and then LED light with awavelength of 405 nm was irradiated at an intensity of 50 mW/cm² for 40seconds. The transparency of the cured product obtained at a wavelengthof 450 nm was measured according to the method set forth in ASTM D1003.

<Cloudiness of Cured Product>

The photocurable liquid silicone composition is filled between two glasssheets with a thickness of 2 mm such that the thickness after curing isapproximately 200 μm (fill area: 20×40 mm²), and then LED light with awavelength of 405 nm was irradiated at an intensity of 50 mW/cm² for 40seconds. The cured product produced between the two glass sheets washeld for 1000 hours in an environment at 85° C. and 85% RH, after whichcloudiness was measured according to the method set forth in ASTM D1003.

<Yellowness of Cured Product>

The yellowness b* of the cured product produced between the two glasssheets that was fabricated for the cloudiness test was measured by themethod according to ASTM D6290. Next, the plate shaped cured product washeld for 1000 hours in an environment at 85° C. and 85% RH, and then theyellowness b* was measured as described above.

<Adhesion of Cured Product>

The photocurable liquid silicone composition was filled between a glasssheet and a polycarbonate sheet with a thickness of 2 mm such that thethickness after curing was approximately 200 μm (fill area: 20×20 mm²),after which LED light with a wavelength of 405 nm was irradiated at anintensity of 50 mW/cm² for 40 seconds. The adhesive strength of thecured product formed between the two glass sheets was measured by themethod according to ASTM D3163 (tensile speed: 100 mm/minute).

Examples 1 to 8 and Comparative Examples 1 to 3

A solvent free photocurable liquid silicone composition was preparedfrom the following components using the composition (parts by mass)shown in Table 1. Note that the photocurable liquid silicone compositionwas prepared and provide 1 mol of 3-mercaptopropyl group in component(B) with regard to 1 mol of vinyl groups in component (A).

The following components were used as component (A). (a-1): adimethylpolysiloxane endblocked at both molecular chain terminals withdimethylvinylsiloxy groups and having a viscosity at 23° C. of 500 mPa·s(a-2): a copolymer of dimethylsiloxane and diphenylsiloxane endblockedat both molecular chain terminals with dimethylvinylsiloxy group, havinga viscosity at 23° C. of 300 mPa·s, and represented by the formula:

Me₂ViSiO(Me₂SiO)₉₅(Ph₂SiO)₅SiMe₂Vi

The following component was used as component (B). (b-1): a copolymer ofdimethylsiloxane and methyl(3-mercaptopropyl)siloxane endblocked at bothmolecular chain terminals with trimethylsiloxy groups, having aviscosity at 23° C. of 100 mPa·s, and represented by the formula:

Me₃SiO(Me₂SiO)₂₆(MeThiSiO)₃SiMe₃

The following component was used as component (C). (c-1): anorganopolysiloxane having a weight average molecular weight of 3,200 andrepresented by the average unit formula:

(Me₃SiO_(1/2))_(0.41)(SiO_(4/2))_(0.59)

The following component was used as component (D). (d-1):diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide

The following component was used as component (E). (e-1):2,6-di-tert-butyl-4-methylphenol

The following component was used as component (F). (f-1): anorganopolysiloxane having an ether group and represented by the averageformula:

Me(EO)₃(OCH₂CH(Me)CH₂)Me₂SiO(Me₂SiO)₁₀(MeViSiO)_(2.5)SiMe₂(CH₂CH(Me)CH₂)(EO)₃OMe

The following component was used as component (G). (g-1): 1-hexadecene

The following components were used as the other arbitrary components.(x-1): 2-hydroxy-2-methyl-1-phenyl-propan-1-one (x-2):1,1,3,3-tetramethyl-1,3-divinyl disiloxane (x-3):1,3,5,7-tetramethyl-1,3,5,7-tetravinyl cyclotetrasiloxane

When preparing the photocurable liquid silicone composition, component(c-1) was prepared by a mixture produced by diluting a 75 mass % xylenesolution thereof with component (a-1) or component (a-2), thencompletely removing the xylene under reduced pressure. Furthermore,component (d-1) was prepared by first diluting in component (x-1).Furthermore, component (e-1) was prepared by first diluting in component(x-2) or component (x-3).

TABLE 1 Comparative Example Example 1 2 3 4 5 6 7 8 1 2 3 Composition of(a-1) 32.60 35.00 40.98 55.15 31.78 29.22 — 15.02 35.00 66.80 —photocurable (a-2) — — — — — — 28.60 — — — 79.60 liquid (b-1) 7.92 8.168.99 10.95 9.71 16.56 18.31 36.33 8.16 12.50 19.70 silicone (c-1) 58.7856.14 49.33 33.20 57.31 52.60 51.48 27.04 56.14 20.00 — composition(d-1) 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 — 0.05 0.05 (parts bymass) (e-1) 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.13 (f-1)— — — — — — — 20.00 — — — (g-1) — — — — 0.50 — — — — — — (x-1) 0.13 0.130.13 0.13 0.13 0.13 0.13 0.13 0.18 0.13 0.13 (x-2) 0.39 0.39 0.39 0.390.39 — — — 0.39 0.39 0.39 (x-3) — — — — — 1.30 1.30 1.30 — — — Viscosity(mPa · s) 19700 8700 2600 740 9000 3500 3070 150 8600 480 230 AppearanceA A A A A A A A A B A Curing properties A A A A A A A A B A ATransparency (%) 98 97 97 97 97 97 98 97 — 95 98 Cloudiness <0.5 <0.5<0.5 <0.5 <0.5 <0.5 <0.5 <0.2 — <0.5 3.8 b* value Initial <0.2 <0.2 <0.2<0.2 <0.2 <0.2 <0.2 <0.2 — <0.2 <0.2 after <0.2 <0.2 <0.2 <0.2 <0.2 <0.2<0.2 <0.2 — <0.2 <0.2 1000 hours

The results of Examples 1 to 8 confirmed that the photocurable liquidsilicone composition of the present invention has favorabletransparency, and even after curing, has high transparency and excellenthigh temperature and high humidity resistance. On the other hand, theresults of Comparative Example 1 confirmed that a photocurable liquidsilicone composition not containing component (D) will not cure by longwavelength light, with the results of Comparative Example 2 confirmingthat the transparency of the cured product is reduced if the amount ofcomponent (C) is insufficient. Furthermore, the results of Example 8confirmed that the photocurable liquid silicone composition containingcomponent (F) of the present invention has favorable transparency, andeven after curing, has high transparency and excellent high temperatureand high humidity resistance.

INDUSTRIAL APPLICABILITY

The photocurable liquid silicone composition of the present inventionquickly cures by irradiation with long wavelength light, for example,visible light having a wavelength of 405 nm, maintains transparency evenwhen left under high temperature and high humidity conditions, and formsa cured film with minimal clouding and discoloration, and therefore isuseful as a protective film or pressure sensitive adhesive for opticaldisplays, and in particular, can also be applied to displays in whichthe cover material is a plastic material such as polycarbonate.

1. A photocurable liquid silicone composition comprising: (A) a straightchain organopolysiloxane with a viscosity at 23° C. of 50 to 100,000mPa·s, containing at least two alkenyl groups with 2 to 12 carbon atomsin a molecule, and not containing a mercaptoalkyl group; (B) anorganopolysiloxane with a viscosity at 23° C. of 10 to 10,000 mPa·s andhaving at least two mercaptoalkyl groups in a molecule, in an amountsuch that the amount of mercaptoalkyl groups in this component is 0.2 to3 moles with regard to 1 mole of alkenyl groups in component (A); (C) abranched chain organopolysiloxane containing siloxane units representedby the formula: R³SiO_(3/2) where R³ represents an alkyl group with 1 to12 carbon atoms, an aryl group with 6 to 20 carbon atoms, an aralkylgroup with 7 to 20 carbon atoms, a hydroxyl group, or an alkoxy groupwith 1 to 6 carbon atoms and/or siloxane units represented by theformula: SiO_(4/2), wherein the molar ratio of siloxane unitsrepresented by the formula: R³SiO_(3/2) and the siloxane unitsrepresented by the formula: SiO_(4/2) of all of the siloxane units incomponent (C) is at least 0.5, and alkenyl groups and mercaptoalkylgroups are not included; (D) a photo radical initiator containing aphosphorus atom; and (E) a hindered phenol compound; wherein the amountof component (C) is 25 to 80 parts by mass, the amount of component (D)is 0.01 to 1.0 parts by mass, and the amount of component (E) is 0.001to 1.0 parts by mass, with regard to 100 parts by mass of a total ofcomponent (A) through component (E).
 2. The photocurable liquid siliconecomposition according to claim 1, further comprising: (F) 1 to 50 partsby mass of an organopolysiloxane having an organic group with an etherbond and an alkenyl group with 2 to 12 carbon atoms in a molecule,however excluding organopolysiloxane corresponding to component (A), andnot having a mercaptoalkyl group, with regard to 100 parts by mass of atotal of component (A) through component (E).
 3. The photocurable liquidsilicone composition according to claim 1, further comprising: (G) 0.1to 10 parts by mass of an organic compound having one aliphaticunsaturated bond in a molecule, and not having a siloxane bond, withregard to 100 parts by mass of a total of component (A) throughcomponent (E).
 4. The photocurable liquid silicone composition accordingto claim 1, wherein the viscosity at 23° C. is 100,000 mPa·s or less. 5.The photocurable liquid silicone composition according to claim 1, whichis a pressure sensitive adhesive composition for optical applications.6. A cured product made by irradiating and curing the photocurableliquid silicone composition according to claim
 1. 7. The photocurableliquid silicone composition according to claim 2, further comprising:(G) 0.1 to 10 parts by mass of an organic compound having one aliphaticunsaturated bond in a molecule, and not having a siloxane bond, withregard to 100 parts by mass of a total of component (A) throughcomponent (E).